Hi, First thing I would say is, don't take any more photo's on that card (yet) to prevent any more damage.
When you see a thumbnail image, it isn't being shown from the photo data, it's coming from a separate block of info in the header, so in a worst case it may be all there is. (maybe),
The free program 'Recuva' is the best of the data recovery programs that I know of, I have got back deleted video with it, so it does work.
If you try 'Recuva' you won't do any harm, just be sure you save (recover) your found jpgs to a different place from the card, the 'C' drive is fine for that.
If you are seeing photo's on a TV connected by lead form camera, is it possible they are not on the SD card, but are saved on the camera's internal memory? So if you take the SD card out can you still see those photo's on the camera screen?
As a backup do make a copy of the DCIM folder somewhere, so if better ideas turn up (or better software) you can work on it in the future.